1. Technical Field
This disclosure is related to formation of conductive features on substrates.
2. Related Art
Transparent conductors refer to thin conductive films coated on high-transmittance surfaces or substrates. Transparent conductors may be manufactured to have surface conductivity while maintaining reasonable optical transparency. Such surface conducting transparent conductors are widely used as transparent electrodes in flat liquid crystal displays, touch panels, electroluminescent devices, and thin film photovoltaic cells, as anti-static layers and as electromagnetic wave shielding layers.
Currently, vacuum deposited metal oxides, such as indium tin oxide (ITO), are the industry standard materials to provide optically transparency and electrical conductivity to dielectric surfaces such as glass and polymeric films. However, metal oxide films are fragile and prone to damage during bending or other physical stresses. They also require elevated deposition temperatures and/or high annealing temperatures to achieve high conductivity levels. There also may be issues with the adhesion of metal oxide films to substrates that are prone to adsorbing moisture such as plastic and organic substrates, e.g. polycarbonates. Applications of metal oxide films on flexible substrates are therefore severely limited. In addition, vacuum deposition is a costly process and requires specialized equipment. Moreover, the process of vacuum deposition is not conducive to forming patterns and circuits. This typically results in the need for expensive patterning processes such as photolithography.
Conductive polymers have also been used as optically transparent electrical conductors. However, they generally have lower conductivity values and higher optical absorption (particularly at visible wavelengths) compared to the metal oxide films, and suffer from lack of chemical and long-term stability.
Recently, transparent conductors formed using conductive nanostructures have been developed and provide some advantages over the types of transparent conductors mentioned above. In particular, transparent conductors formed using conductive nanostructures are relatively flexible, can be fabricated using wet coating processes and can exhibit desirable electrical and optical characteristics. Such transparent conductors and disclosed, for example, in U.S. patent application Ser. Nos. 11/766,552; 11/504,822; 11/871,767; and 11/871,721 which are incorporated by reference herein in their entirety. Additionally, while a number of the device applications mentioned above can use transparent conductive sheets having a relatively large, contiguous conductive area, many of these applications also require layers in which relatively smaller areas, patterns, traces, lines or other such features are conductive. While methods have been developed to pattern nanostructure based transparent conductors, such patterning processes may present manufacturing inefficiencies. Accordingly, there is a need to be able to produce nanostructure based conductive films having conductive patterns or features.